Furnace assembly for a metal-making process

ABSTRACT

A furnace assembly for a metal-making process, including: an electric arc furnace configured for flat bath operation and having a bottom, and an electromagnetic stirrer configured to be arranged underneath the bottom of the electric arc furnace to enable stirring of molten metal in the electric arc furnace.

TECHNICAL FIELD

The present disclosure generally relates to metal-making and inparticular to a furnace assembly for a metal-making process.

BACKGROUND

Flat bath operation (FBO) is a process of continuously feeding orsmall-bucket charging of metallic materials such as scrap, pig iron,direct reduced iron (DRI), hot metal, or hot briquetted iron (HBI), intothe furnace bath of an electric arc furnace (EAF) without opening thefurnace roof. During the metallic charging, the electric arc iscontinuously powered and the metallic materials are continuously meltedin the bath. This process provides high energy efficiency and lesselectrode consumption.

One issue of a flat bath melting process is the temperaturehomogenization of the furnace bath, especially in the metal chargingarea which is always a cold zone. Incomplete metal-melting in the coldzone creates potential problems such as concentration gradients,unreliable measurements, unsafe process control, superheated bath, andover tap temperature. To solve this inhomogeneous temperature problem,bath stirring is recommended to improve the melt convection. To thisend, bottom gas stirring by porous plugs has been implemented in thesome of these furnaces.

For bottom gas stirring, porous plugs with direct or indirect gaspurging are installed in the bottom refractory. Normally 3-5 porousplugs are needed depending on the furnace size. The stirring intensityis controlled by the gas, typically nitrogen or argon, and by flow rateand pressure.

SUMMARY

There are some challenges with bottom gas stirring. For example, theremay be incomplete bath mixing with dead zones far from the plugs,resulting in limited homogenization in the furnace bath. Furthermore,the stirring pattern and direction are fixed by the plug positions withlimited horizontal flow velocity. Moreover, the refractory wearingaround the porous plug is more serious and the plugs on the bottom arerisk points for melt breakout. Finally, the lifespan of the porous plugis often shorter than that of the bottom lining campaign, and onlinemaintenance for porous plugs is a difficult and complicated work.

In view of the above, an object of the present disclosure is to providea furnace assembly for a metal-making process which solves, or at leastmitigates, the problems of the prior art.

There is hence provided a furnace assembly for a metal-making process,comprising: an electric arc furnace configured for flat bath operationand having a bottom, and an electromagnetic stirrer configured to bearranged underneath the bottom of the electric arc furnace to enablestirring of molten metal in the electric arc furnace.

An effect which may be obtainable thereby is that stirring within theentire melt bath with no dead zone or essentially no dead zone in thebath may be provided. Hence, more efficient metal-making using anelectric arc furnace configured for flat bath operation may be provided.

Moreover, there is no negative effect on the refractory lining and nomolten metal breakout risk, as is the case with porous plugs.Additionally, the long lifespan of the electromagnetic stirrer coilrequires almost no maintenance.

The electromagnetic stirring reduces the melt surface superheat and theheat from the arc zone is quickly transmitted to the bulk melt. Thedecrease of surface superheat temperature reduces the heat losses to thefurnace wall and roof during the power on period, which thereby reducesthe electricity consumption. Another advantage of superheat reductionduring power on is less refractory wearing in the slag-line area of theelectric arc furnace.

A further effect provided by the electromagnetic stirrer on the electricarc furnace with flat bath operation process is that the processreliability is significantly improved. The fast melt-down of e.g. scrapand ferrochromium provides a quick homogenization of the melt bath onboth chemical composition and temperature, which ensures the targetedsteel tapping weight and temperature. Homogeneous temperature in thewhole bath provides a smooth tapping and reduces tapping delays. Theelimination of thermal stratification in the melt bath also reduces thetapping temperature. High eccentric bottom tapping free openingfrequency is a very important benefit both for the operation safety andproductivity.

According to one embodiment the electric arc furnace has ametal-charging region, wherein the electromagnetic stirrer is configuredto be arranged to provide stirring of molten metal in the metal-chargingregion.

The metal-charging region is a region of the interior of the electricarc furnace, which receives the charged metallic material. It includes aportion of the bottom of the electric arc furnace where the metallicmaterial fed to the electric arc furnace is initially accumulated beforebeing melted by the heat in the electric arc furnace and mixed with therest of the melt by stirring of the electromagnetic stirrer.

According to one embodiment the metal-charging region is locatedoff-center with respect to a center point of the bottom of the electricarc furnace.

According to one embodiment the electromagnetic stirrer comprises coilsconfigured to generate a traveling magnetic field in a first directionalong a stirring direction axis, wherein the electromagnetic stirrer isconfigured to be arranged so relative to a central plane extendingthrough the center of the electric arc furnace and through a tappinghole or spout of the electric arc furnace that the stirring directionaxis is at an angle relative to the central plane.

The first direction, which defines the stirring direction axis along astirring direction of molten metal in the electric arc furnace, henceintersects the central plane. The central plane is a vertical plane whenthe arc furnace is in operation, i.e. when in a tap-to-tap meltingcycle.

In this manner, the stirring force will be directed directly towards themetal-charging region, and thus more efficient stirring in the alwayscold metal-charging region or area may be obtained. Cold here meanscooler than the rest of the melt.

According to one embodiment the angle is in the range of 0° and 90°.

According to one embodiment the angle is 90°.

According to one embodiment the angle is greater than 0° and less than90°.

The stirring force created by the electromagnetic stirrer will therebybe directed towards the metal-charging region cold scrap zone area witha selectable angle in the range of 0 to 90 degrees. This electromagneticstirrer configuration will create a melt flow towards or backwards thecold metal-charging region or zone in the furnace which greatly improvesthe metal-melting and furnace temperature homogenization.

According to one embodiment the electromagnetic stirrer is arrangedcentered underneath the electric arc furnace.

According to one embodiment the electromagnetic stirrer is arrangedoff-center underneath the electric arc furnace.

One embodiment comprises an electromagnetic stirrer position controllerconfigured to control the orientation of the electromagnetic stirrerrelative to the electric arc furnace to thereby adjust the angle.

By being able to change the stirring direction more flexible control maybe provided. For example, by orienting the electromagnetic stirrer witha certain angle relative to the central plane sufficient global stirringof the melt may be provided, i.e. also in the metal-charging region,while the stirring may reduce vortex formation above the tapping hole,in the manner disclosed in EP2751510.

One embodiment comprises a frequency converter configured to control thecurrent in the electromagnetic stirrer, and a control system configuredto control the frequency converter.

According to one embodiment the electric arc furnace is configured toreceive charging of metallic material from a side of the electric arcfurnace.

According to one embodiment the electric arc furnace is configured toreceive charging of metallic material from above the electric arcfurnace.

According to one embodiment the electric arc furnace is configured toreceive continuous charging of the metallic material.

The electric arc furnace may for example be configured to receivecontinuous charging of the metallic material by means of a conveyor beltor a runner. Alternatively, or additionally, the electric arc furnacemay be configured to receive continuous charging of the metallicmaterial from a hole in the roof of the electric arc furnace. Hereto,the roof, or furnace roof, may be provided with a through-opening orhole to allow for top feeding of metallic material into the electric arcfurnace.

According to one embodiment the electric arc furnace is configured toreceive bucket charging of the metallic material through a shaft.

Generally, all terms used in the claims are to be interpreted accordingto their ordinary meaning in the technical field, unless explicitlydefined otherwise herein. All references to a/an/the element, apparatus,component, means, etc. are to be interpreted openly as referring to atleast one instance of the element, apparatus, component, means, etc.,unless explicitly stated otherwise.

BRIEF DESCRIPTION OF THE DRAWINGS

The specific embodiments of the inventive concept will now be described,by way of example, with reference to the accompanying drawings, inwhich:

FIG. 1 schematically shows a partly transparent top view of an electricarc furnace, and an electromagnetic stirrer provided below the electricarc furnace; and

FIGS. 2a-2b, 3a-3b, 4a-4b, and 5a-5b schematically show various exampleof furnace assemblies in a partially transparent top view and in crosssection.

DETAILED DESCRIPTION

The inventive concept will now be described more fully hereinafter withreference to the accompanying drawings, in which exemplifyingembodiments are shown. The inventive concept may, however, be embodiedin many different forms and should not be construed as limited to theembodiments set forth herein; rather, these embodiments are provided byway of example so that this disclosure will be thorough and complete,and will fully convey the scope of the inventive concept to thoseskilled in the art. Like numbers refer to like elements throughout thedescription.

The present disclosure relates to a furnace assembly for a metal-makingprocess. The metal-making process may for example be a steel-makingprocess, an aluminum-making process, or lead-making process.

The furnace assembly comprises an electric arc furnace and anelectromagnetic stirrer configured to be arranged underneath theelectric arc furnace to thereby enable stirring of molten metal in theelectric arc furnace. The electromagnetic stirrer may for example beconfigured to be mounted onto the electric arc furnace rockers andconfigured to be rotated together with an electric arc furnace tiltingsystem, or the electromagnetic stirrer may for example be configured tobe mounted underneath the electric arc furnace on a separate supportstructure, for example on a trolley, which is configured to bestationary or to rotate synchronously with the bottom of the electricarc furnace upon a tapping operation.

The herein presented electric arc furnace is configured for flat bathoperation. Hereto, the electric arc furnace is configured to receivemetal in a continuous manner during a tap-to-tap cycle. To this end, theelectric arc furnace is configured to be charged continuously with metalduring a tap-to-tap cycle. The charging assembly and the electric arcfurnace may for example be configured for a Consteel®, Quantum®, or anEcoArc® procedure/assembly, or for continuous DRI feeding from the roofof the electric arc furnace. The electric arc furnace may hence forexample be configured to be charged with metallic material from the sideof the electric arc furnace, in which case the electric arc furnace maybe configured as a shaft furnace. Or the electric arc furnace may beconfigured to be charged with metallic material from the roof. Themetallic material may either be pre-heated, hot or cold.

FIG. 1 schematically shows a partially transparent top view of anexample of a furnace assembly 1 for metal-making. The furnace assembly 1comprises an electric arc furnace 3 having a body or furnace shellconfigured to receive and hold metallic material during a tap-to-tapcycle.

The body or furnace shell is furthermore configured to receive aplurality of electrodes arranged to be lowered into the body or furnaceshell to melt any metallic material contained therein.

The electric arc furnace 3 comprises a bottom 3 a having a tapping hole3 b, or alternatively or additionally a spout 3 c, in order to enabletapping of the heat of metal from the body or furnace shell. In case ofa variation which includes a tapping hole 3 b, the tapping hole 3 b isarranged offset, or off-center, relative to the center point of thebottom 3 a of the furnace shell.

The furnace assembly 1 furthermore comprises an electromagnetic stirrer5. The bottom 3 a of the electric arc furnace 3 comprises a non-magneticwindow, beneath which the electromagnetic stirrer 5 is configured to beinstalled. The non-magnetic window may for example comprise austeniticstainless steel, or any other kind of non-magnetic metallic material.

The electromagnetic stirrer 5 comprises a magnetic core and coilsarranged around the magnetic core, not shown. The coils may beconfigured to be connected to a respective electric phase of an ACcurrent supply so that the electromagnetic stirrer 5 can be fed with apoly-phase low frequency AC current. The coils are thus configured suchthat when suitably fed with a respective AC current, a travelingmagnetic field is generated along a stirring direction axis 9.

In operation, the low frequency AC current through the coils generates atraveling magnetic field which penetrates the electric arc furnacebottom and thereby generates forces in the molten metal or melt. Sincethe magnetic field penetrates the whole depth of the melt, the melt willflow in the same direction, along the stirring direction axis 9, acrossthe entire diameter/width of the electric arc furnace and down to thewhole depth of the bath. After reaching the electric arc furnace wallthe melt will flow back along the sides of the electric arc furnace.

Furthermore, in FIG. 1, a central plane 7 is shown, extending throughthe center point of the bottom 3 a and through the center of the tappinghole 3 b, or in case of a presence of a spout 3 c, through the center ofthe spout 3 c. This plane is typically a vertical plane when the furnaceassembly 1 has been installed in a metal works or metal mill, forexample a steel mill or an aluminum mill.

The electromagnetic stirrer 5 is configured so that there is an angle αbetween the central plane 7 and the stirring direction axis 9 whichintersects the central plane 7. In the example shown in FIG. 1, theangle α is 90°.

According to one variation, the angle α between the central plane 7 andthe stirring direction axis 9 may be in the range of 0° and 90°. Forexample, the angle α may be 0°, or the angle α may be more than 0° butless than 90°. In this latter case, the electromagnetic stirrer 5 wouldbe inclined or arranged obliquely with respect to the central plane 7.The electromagnetic stirrer 5 may be arranged centered underneath theelectric arc furnace with respect to the center of the electric arcfurnace, or it may be arranged off-set from the center.

The orientation of the electromagnetic stirrer relative to the centralplane 7 may be adjusted, either manually or in an automated manner. Forexample, the furnace assembly may comprise an electromagnetic stirrerposition controller configured to control the orientation of theelectromagnetic stirrer 5 relative to the electric arc furnace 3, and inparticular relative to the central plane 7, to thereby adjust the angleα. The angle α may for example be adjusted or controlled based on theinstantaneous amount of global stirring of the melt necessary and basedon the need of vortex reduction above the tapping hole 3 a, in the eventthat the electric arc furnace 3 has a tapping hole. The orientation ofthe electromagnetic stirrer 5 may thus be a trade-off between optimalglobal stirring and vortex reduction.

The electric arc furnace 3 also has a metal-charging region 11, which isa region of the bottom 3 a of the body or furnace shell where themetallic material charged continuously into the furnace shell isinitially accumulated in the electric arc furnace 3. The metal-chargingregion 11 may be arranged off-center with respect to center of thebottom 3 a, as shown in the example in FIG. 1. Alternatively, themetal-charging region 11 may be arranged at the center or essentially atthe center of the bottom 3 a.

In case the electric arc furnace is configured to be charged withmetallic material through a through-opening or hole in the furnace roof,the metal-charging region 11 will typically not be at bottom of the bodyor furnace shell, but on the surface or meniscus of the melt. In thiscase, the metal-charging region may be arranged center or off-centeredin a horizontal section of the electric arc furnace.

The electromagnetic stirrer 5 is arranged so that the stirring forcecreated by the electromagnetic stirrer 5 is directed towards the coldzone formed by the metal-charging region 11, or at an angle of up to 90°depending on the orientation of the electromagnetic stirrer 5 relativeto the central plane 7. It is thereby possible to create a melt flowtowards or backwards the metal-charging region 11 in the electric arcfurnace 3, which greatly improves the metal-melting and temperaturehomogenization compared to the use of, or without use of, porous plugsin combination with gas. As previously noted, the electromagneticstirrer 5 may be arranged centered underneath the electric arc furnace,or it may be arranged off-center. In the latter case, theelectromagnetic stirrer may for example be arranged underneath themetal-charging area 11, with the angle α anywhere between 0° and 90°degrees relative to the central plane 7.

The furnace assembly may comprise a power converter, typically afrequency converter, not shown, configured to control the current in thecoils of the electromagnetic stirrer, to thereby control the stirring ofthe molten metal or melt contained in the furnace shell. In this case,the furnace assembly may also comprise a control system configured tocontrol the frequency converter to thereby control the current in theelectromagnetic stirrer.

Various examples of a furnace assembly will now be shown with referenceto FIGS. 2a-2b, 3a-3b, 4a-4b, and 5a -5 b.

FIG. 2a shows a partially transparent bottom view of an example of afurnace assembly 1 with flat bath operation. The exemplified furnaceassembly 1-1 is continuously fed with metallic material from the side ofthe furnace shell by means of a conveyor belt 4. The electromagneticstirrer 5 is arranged below the bottom of the electric arc furnace 3.The electromagnetic stirrer 5 shown with solid lines is depicted with anangle α that is 90° relative to the central plane 7 shown in FIG. 1. Theelectromagnetic stirrer 5 is also shown with another orientation, withdashed lines, where the angle α is 0° relative to the central plane 7.The electromagnetic stirrer 5 may be configured to be oriented with anyangle α between 0° and 90° or with essentially any angle α between 0°and 90°. For example, if the electromagnetic stirrer is motor-driven,not all angles may be possible to be attained and the actual orientationmay be dependent upon the resolution provided by the electromagneticstirrer position controller.

In FIG. 2b , a cross-sectional view of the furnace assembly 1-1 isshown, with the cross-section being taken at lines A-A in FIG. 2a .Here, the electrodes 13 which are submerged in the melt M are alsoshown, as well as the metal-charging region 11. According to thisexample, the metallic material may be charged continuously into furnaceshell or body by means of a conveyor belt 4 moving from the side towardsthe electric arc furnace 3.

FIG. 3a shows a partially transparent top view of another example of afurnace assembly 1 with flat bath operation. The exemplified furnaceassembly 1-2 is fed with metallic material from the top to e.g. anoff-center location in the electric arc furnace 3, via a shaft 15arranged above the electric arc furnace 3. The electromagnetic stirrer 5may again be able to be oriented within 0° and 90° relative to thecentral plane 7 shown in FIG. 1. FIG. 3b shows the furnace assembly 1-2through the cross-section taken at lines B-B.

FIG. 4a shows a partially transparent top view of another example of afurnace assembly 1 with flat bath operation. The exemplified furnaceassembly 1-3 is continuously fed with metallic material from the sidevia a conveyer belt 4, and it is also charged from the top via a shaft15 arranged above the electric arc furnace 3. Feeding may be providedalternatingly by means of the conveyor belt and the shaft, orsimultaneously. In this example, the electric arc furnace has a spoutfor tapping the melt, but could alternative be provided with a tappinghole.

The electromagnetic stirrer 5 may also in this case be configured to beoriented within 0° and 90° relative to the central plane 7 shown inFIG. 1. FIG. 4b shows the furnace assembly 1-3 through the cross-sectiontaken at lines C-C.

FIG. 5a shows a partially transparent top view of another example of afurnace assembly 1 with flat bath operation. The exemplified furnaceassembly 1-4 is continuously fed with metallic material from above theelectric arc furnace 3 by means of a conveyor belt or a runner. The roofof the electric arc furnace 3 is provided with a through-opening 16,i.e. a feeding hole, for example the “5th hole”, for feeding metallicmaterial into the electric arc furnace 3 by means of the conveyor beltor the runner. The metallic material may for example comprise or bedirect reduced iron.

The electromagnetic stirrer 5 may like previously having been described,be able to be oriented within 0° and 90° relative to the central plane 7shown in FIG. 1. FIG. 5b shows the furnace assembly 1-3 through thecross-section taken at lines D-D.

The metallic material used for continuous feeding may for example bescrap, ferroalloys, direct reduced iron, hot briquetted iron, pig iron,hot metal, or mixing of metallic materials and oxides.

The inventive concept has mainly been described above with reference toa few examples. However, as is readily appreciated by a person skilledin the art, other embodiments than the ones disclosed above are equallypossible within the scope of the inventive concept, as defined by theappended claims.

The invention claimed is:
 1. A furnace assembly for a metal-making process, comprising: an electric arc furnace configured for flat bath operation and having a bottom, and an electromagnetic stirrer configured to be arranged underneath the bottom of the electric arc furnace to enable stirring of molten metal in the electric arc furnace, wherein a metal-charging region is located off-center with respect to a center point of the bottom of the electric arc furnace, and wherein the electromagnetic stirrer includes coils configured to generate a traveling magnetic field in a first direction along a stirring direction axis when fed with a respective AC current, wherein the electromagnetic stirrer is configured to be arranged relative to a central plane extending through the center of the electric arc furnace and through a tapping hole or spout of the electric arc furnace so that the stirring direction axis is at an angle relative to the central plane, wherein the stirring direction axis intersects the central plane.
 2. The furnace assembly as claimed in claim 1, wherein the angle is 90°.
 3. The furnace assembly as claimed in claim 1, wherein the angle is greater than 0° and less than 90°.
 4. The furnace assembly as claimed in claim 1, wherein the electromagnetic stirrer is arranged centered underneath the electric arc furnace.
 5. The furnace assembly as claimed in claim 1, wherein the electromagnetic stirrer is arranged off-center underneath the electric arc furnace.
 6. The furnace assembly as claimed in claim 1, comprising an electromagnetic stirrer position controller configured to control an orientation of the electromagnetic stirrer relative to the electric arc furnace to thereby adjust the angle.
 7. The furnace assembly as claimed in claim 1, comprising a frequency converter configured to control the current in the electromagnetic stirrer, and a control system configured to control the frequency converter.
 8. The furnace assembly as claimed in claim 1, wherein the electric arc furnace is configured to receive charging of metallic material from a side of the electric arc furnace.
 9. The furnace assembly as claimed in claim 1, wherein the electric arc furnace is configured to receive charging of metallic material from above the electric arc furnace.
 10. The furnace assembly as claimed in claim 8, wherein the electric arc furnace is configured to receive continuous charging of the metallic material.
 11. The furnace assembly as claimed in claim 8, wherein the electric arc furnace is configured to receive bucket charging of the metallic material through a shaft.
 12. The furnace assembly as claimed in claim 1, wherein the bottom of the electric arc furnace comprises a non-magnetic window, beneath which the electromagnetic stirrer is configured to be arranged.
 13. The furnace assembly as claimed in claim 12, wherein the non-magnetic window comprises a non-magnetic metallic material.
 14. The furnace assembly as claimed in claim 6, wherein the electromagnetic stirrer position controller is configured to adjust the angle based on an instantaneous amount of global stirring of a melt necessary.
 15. The furnace assembly as claimed in claim 14, wherein the electromagnetic stirrer position controller is configured to adjust the angle based on a need for vortex reduction above the tapping hole.
 16. The furnace assembly as claimed in claim 1, wherein a stirring force created by the electromagnetic stirrer is directed towards a cold zone formed by the metal-charging region.
 17. The furnace assembly as claimed in claim 1, wherein the tapping hole is arranged off-center with respect to the center point of the bottom of the electric arc furnace.
 18. The furnace assembly as claimed in claim 1, wherein the coils are connected to a respective electric phase of an AC current supply.
 19. The furnace assembly as claimed in claim 1, wherein the electromagnetic stirrer is fed with a poly-phase AC current. 